The new company will be a be a network of more than 4,000 employees across 42 countries.

Sorrell says: “Our decision to merge the two agencies is driven by strong, compatible capabilities and expertise, a combined ability to deliver integrated solutions across multiple sectors and the scale to compete with the largest communications agencies in the world.

“We have a major opportunity and the right team to take this new agency to even higher levels of success. After years of strong leadership and delivering excellent results at Cohn & Wolfe, I know that Donna will ensure the success of the combined business. I would also like to thank Don for his contribution as CEO of Burson-Marsteller over the last six years. I know he will continue his dedication to serving clients and now be able to focus entirely on high-level counsel to those clients as chairman.”

Imperato says: “The launch of Burson Cohn & Wolfe creates a new entity in the world of communications that offers our clients unparalleled, integrated digital solutions grounded in earned media. We are energized by the fresh offerings we will bring to both our clients and our employees.”

Independently-owned Edelman is the world’s biggest PR company.

The moves follows the merger of Maxus into MEC to form the new Wavemaker among WPP’s media agencies and the grouping of various Kantar research businesses into Kantar Consulting. So far Sorrell has resisted any temptation to merge his creative agencies which include Grey, JWT, Ogilvy and Y&R. All of these were acquired for huge sums as WPP built the world’s biggest marcoms company.